1. Field of the Invention
This invention relates generally to an apparatus for the percutaneous positioning of an imaging marker for identifying the location of a lesion in a biopsy procedure. More particularly, the invention relates to a self-contained marking apparatus that expels the imaging marker through the side of the marking device.
2. Description of the Related Art
Tissue biopsies are commonly performed on many areas and organs of the body where it is desirable to ascertain whether or not the biopsied tissue is cancerous. Often, a lesion or other tissue to be biopsied is identified through use of an imaging technique such as a computerized axial tomography (CAT) scan, ultrasonography, magnetic resonance imaging, and mammography.
One problem commonly encountered, especially in breast biopsies, is that the lesion is so small that the biopsy reduces its size to the extent that it is no longer visible by the imaging method employed. In such circumstances, it is desirable to place an imaging marker at the site of the biopsy to enable the medical practitioner subsequently to locate the lesion quickly and accurately in the event complete removal of the affected tissue is indicated. This problem is currently met by placing an imaging marker at the biopsy area by means of a cannula or similar device housing the marker.
There are currently two primary types of marking devices. One of the primary types is referred to as vacuum assisted biopsy devices (VAB's). The VAB devices are many times integrated with a mammography imaging system. They include a large diameter cannula, approximately 9 to 12 gage, or probe that is inserted into the breast tissue. Instruments, such as a biopsy device and a marking device, are introduced into the breast tissue through the large diameter cannula to take biopsy samples or mark a biopsy location.
The other primary type is self-contained marking devices comprising a small diameter, approximately 14 to 17 gage, open-end cannula and a stylet slidably received within the cannula. A marker is located in the cannula and expelled out the open-end upon the advancing of the stylet relative to the cannula.
One disadvantage of the VAB system is the biopsy and marking tools are integrated with the mammography imaging system. The capital investment of this type of system is substantial. Also, the biopsy and marking tools are typically designed to work only with the large diameter probe, which tends to lock the hospital or medical professional into the same source for the imaging system and the biopsy and marking tools. The VAB systems are also intended for the same components to be reused, which requires sterilization after each step. The various components are also typically flexible to help insert them through the probe. The VAB systems also have a relatively large diameter probe, which, all things being equal, the larger the diameter, the greater trauma to the surrounding tissue and the greater the pain or discomfort for the patient.
The self-contained marking devices address these disadvantages of the VAB systems. Since the self-contained marking device is not integrally incorporated with a particular imaging system, the self-contained marking devices can be used with any suitable imaging system and are not limited to just mammography. This permits the hospital or medical professional to mix and match the available imaging systems and self-contained marking devices to obtain the desired performance and cost-effectiveness.
The self-contained marking devices are typically disposable, which negates the need to sterilize them after each use. They also have a much smaller diameter, resulting in much less trauma to the surrounding tissue and pain to the patient.
A disadvantage of the self-contained systems is that the cannula has an open tip through which the marker is expelled. The open tip is generally closed by the marker residing in the cannula. However, the marker does not completely close off the open tip and it is possible for tissue to enter the open end of the cannula during the positioning of the marking device. The presence of tissue inside the open end of the cannula can interfere or make more difficult the expelling of the marker from the cannula.
The possibility for tissue being present in the open end of the cannula is, to some extent, related to the distance that the cannula is inserted through the tissue to the marking site. Thus, the manner in which the marking device is located at the biopsy site can impact the presence of tissue in the open end of the cannula. For example, the self-contained systems are sometimes used in combination with a positioning cannula that is inserted into the tissue mass with a stylet closing the end of the positioning cannula. In such a configuration, the stylet is removed once the positioning cannula is properly located relative to the biopsy site. Both the biopsy device and the marking device can be inserted and withdrawn through the positioning cannula. The use of the positioning cannula reduces the distance that the open end of the marking device cannula must travel through the tissue.
Alternatively, the marking device can be inserted without the positioning cannula. This is most common when it is desirable to place a marker without taking a biopsy. Under such circumstances, it is more likely that tissue will be received within the open end of the cannula. Therefore, it is more likely that the tissue will interfere with the expelling of the marker.
Therefore, it is desirable to have a self-contained marking device that can be used with or without a positioning cannula and which does not receive tissue within the open end of the cannula that might interfere with the expelling of the marker.